The Clinical Retrovirology Core Unit will continue to provide virologic support to ongoing research on the epidemiologic, immunobiologic, experimental pathogenesis, and basic clinical molecular core virology of HIV transmission and early infection. Specially, this support includes HIV-1 isolation and quantification by microculture, DNA and RNA detection and quantification, and antiretroviral drug sensitivity testing, syncytium-inducing phenotype, and serologic procedures for HIV-1 antibody, p24 antigen, and HIV-1 neutralization. The laboratory has taken a leading role in developing sensitive HIV culture techniques for both peripheral blood mononuclear cells and plasma, and has contributed important work on the pathogenesis of HIV infection by studying the natural history of HIV plasma viremia and the measurement of quantitative changes in plasma HIV to assess the efficacy of antiretroviral therapy. The laboratory has also contributed to our understanding of the shedding of HIV in the semen of HIV-infected men. The University of Washington Virology Laboratory has also served as a regional laboratory for he ACTG program during the years 1986-present for performing quantitative HIV-1 assays. It has demonstrated technical expertise in a wide variety of virologic methods and has been instrumental in the design of the ACTG virology program, the computerized data management program and the quality assessment programs, because of its scientific leadership and technical expertise. The University of Washington Retrovirology Laboratory is a model for the type of clinical core laboratory outlined in this proposal.